ATLANTA – An ex-convict fatally shot his 2-year-old son before turning his gun on himself Wednesday at the end of an 18-hour standoff in Atlanta's northeastern suburbs, police said.

Thy Ho, 43, and son Philip Nguyen were each found with a gunshot wound when authorities entered the master bedroom of the Buford home after hearing gunfire about 4:40 p.m. Wednesday, Gwinnett County police Cpl. Michele Pihera said. Pihera said Ho shot himself when officers entered the room.

Both were taken the hospital in critical condition, Pihera said, and later died.

Police said investigators are still processing the crime scene and the Gwinnett County medical examiner will determine the official causes of death.

The Atlanta Journal-Constitution reported that the standoff began Tuesday night after Ho got into an argument with his girlfriend. The paper reported that the girlfriend's teenage son called police at around 10 p.m. local time to reported that Ho was threatening to shoot everyone at the home and then take his own life.

Ho's girlfriend, her son, and "several other people" were allowed to leave the home, but the toddler remained inside with the suspect, police said.

WAGA reported that Philip Nguyen is the son of Ho and his girlfriend. The couple are not married.

A SWAT team sealed off the neighborhood where the "barricaded gunman" was inside the home in a subdivision about 35 miles northeast of downtown Atlanta. Police announced that residents were being allowed back into the neighborhood Wednesday night.

Wednesday was the first day of a new semester in the county's schools after the holidays but school buses were not allowed into the neighborhood, which was on lockdown, school system spokeswoman Sloan Roach said.

The Atlanta Journal-Constitution reported that Ho had served four months in a Georgia prison in 2012 after being convicted of theft by receiving stolen property. Two years earlier, he had been added to the state's sex offender registry after being found guilty in Indiana on a charge of criminal confinement.

The standoff came one day after police in nearby DeKalb County said a man with a knife held 11 children and his girlfriend inside a motel room for five hours before stabbing himself in the neck Tuesday morning. The man was critically injured No one else was hurt.